RFR: 8351187: Add JFR monitor notification event

[David Holmes]

On Tue, 4 Mar 2025 16:05:36 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> We have `JavaMonitorWait` event, but no symmetric `JavaMonitorNotify` event. Notifications are important/interesting to track as well, for example to correlate the delay between notification and eventual wake up.
> 
> Providing this event would also replace one of of the RT counters that are going away in [JDK-8348829](https://bugs.openjdk.org/browse/JDK-8348829).
> 
> This counter is disabled by default to keep any potential impact low. We can consider flipping it to enabled by default later.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `jdk_jfr`

Again a reasonable idea but note that notifications can occur much more frequently than waits. A wait only happens when a thread actually has to wait, whereas notifications tend to happen whenever a data structure is updated in a key way

-------------

PR Review: https://git.openjdk.org/jdk/pull/23901#pullrequestreview-2660126462